The Archaeological Institute of America's members include professional archaeologists, students, and non-professional enthusiasts. The association supports archaeologists and promotes public understanding of the material record of the human past.
The American Classical League promotes the study of classical languages in the U.S. and Canada. Members include (but aren't limited to) teachers of Greek, Latin, and Classics.
Formerly the American Philological Association, the Society for Classical Studies is an association mostly of university and college Classics teachers.
The Classical Association of the Middle West and South is an organization of Latin and Greek teachers at all levels of education, as well as non-teachers with an interest in the Classical world.
Pleiades is a community-maintained site that allows you to find on a map the locations of places and geographical features of the ancient Mediterranean world, along with information about them and connections to other places.
The Perseus Digital Library is an open access collection hosted by the Department of Classical Studies at Tufts University. While the library holds multiple collections, the flagship collection centers on the Greco-Roman world.